In contrast to our finding [1], Mohsenifar and colleagues [2] found respiratory frequency, tidal volume, and the ratio of frequency/tidal volume to be poor predictors of weaning failure. In their important paper on the methodologic standards used in studies of predictive indexes, Wasson and colleagues [3] emphasized the need for investigators to follow the original protocol, but Mohsenifar and associates fell short. First, frequency and tidal volume were measured at 20 to 30 minutes into the weaning trial rather than at the beginning of the trial. Second, they failed to indicate 1) the instrumentation used to measure tidal volume; 2) the sampling period; or 3) the gas being inhaled. Third, they measured frequency and tidal volume during pressure support of “about 7 to 8 cm H2O,” a level judged to overcome resistance of the endotracheal tube and circuit. However, as they reported, this level markedly overcompensates, causing a 39% decrease in work of breathing and a decrease in the ratio of frequency/tidal volume of 14 breaths/min per liter [4]. Thus, it is hardly surprising that the ratio measured during pressure support but using the threshold value derived during spontaneous breathing was inaccurate in predicting weaning failure. Fourth, frequency, tidal volume, and the ratio of frequency/tidal volume were prospectively tested, whereas gastric pH was evaluated in a post hoc manner, which can markedly overestimate the accuracy of a predictive index [3].